The inferior frontal gyrus (IFG; also gyrus frontalis inferior) is the lowest positioned
gyrus
In neuroanatomy, a gyrus (: gyri) is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci (depressions or furrows; : sulcus). Gyri and sulci create the folded appearance of the brain in humans and other mammals.
...
of the
frontal gyri, of the
frontal lobe
The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a Sulcus (neur ...
, and is part of the
prefrontal cortex
In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. It is the association cortex in the frontal lobe. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, ...
.
Its superior border is the
inferior frontal sulcus (which divides it from the
middle frontal gyrus
The middle frontal gyrus makes up about one-third of the frontal lobe of the human brain. (A gyrus is one of the prominent "bumps" or "ridges" on the cerebral cortex
The cerebral cortex, also known as the cerebral mantle, is the outer la ...
), its inferior border is the
lateral sulcus
The lateral sulcus (or lateral fissure, also called Sylvian fissure, after Franciscus Sylvius) is the most prominent sulcus (neuroanatomy), sulcus of each cerebral hemisphere in the human brain. The lateral sulcus (neuroanatomy), sulcus is a deep ...
(which divides it from the
superior temporal gyrus
The superior temporal gyrus (STG) is one of three (sometimes two) gyri in the temporal lobe of the human brain, which is located laterally to the head, situated somewhat above the external ear.
The superior temporal gyrus is bounded by:
* the l ...
) and its posterior border is the
inferior precentral sulcus. Above it is the
middle frontal gyrus
The middle frontal gyrus makes up about one-third of the frontal lobe of the human brain. (A gyrus is one of the prominent "bumps" or "ridges" on the cerebral cortex
The cerebral cortex, also known as the cerebral mantle, is the outer la ...
, behind it is the
precentral gyrus
The precentral gyrus is a prominent gyrus on the surface of the posterior frontal lobe of the brain. It is the site of the primary motor cortex that in humans is cytoarchitecturally defined as Brodmann area 4.
Structure
The precentral gyrus li ...
.
The inferior frontal gyrus contains
Broca's area
Broca's area, or the Broca area (, also , ), is a region in the frontal lobe of the dominant Cerebral hemisphere, hemisphere, usually the left, of the Human brain, brain with functions linked to speech production.
Language processing in the brai ...
, which is involved in
language processing
In psycholinguistics, language processing refers to the way humans use words to communicate ideas and feelings, and how such communications are processed and understood. Language processing is considered to be a uniquely human ability that is ...
and
speech production
Speech production is the process by which thoughts are translated into speech. This includes the selection of words, the organization of relevant Grammar, grammatical forms, and then the articulation of the resulting sounds by the motor system usi ...
.
Structure
The inferior frontal gyrus is highly convoluted and has three
cytoarchitecturally diverse regions.
The three subdivisions are an opercular part, a triangular part, and an orbital part. These divisions are marked by two rami arising from the
lateral sulcus
The lateral sulcus (or lateral fissure, also called Sylvian fissure, after Franciscus Sylvius) is the most prominent sulcus (neuroanatomy), sulcus of each cerebral hemisphere in the human brain. The lateral sulcus (neuroanatomy), sulcus is a deep ...
.
The ascending ramus separates the opercular and triangular parts.
The anterior (horizontal) ramus separates the triangular and orbital parts.
* Opercular part of inferior frontal gyrus (pars opercularis), (cortex posterior to the ascending ramus of the lateral sulcus), is the part of frontal lobe that overlies the
insular cortex
The insular cortex (also insula and insular lobe) is a portion of the cerebral cortex folded deep within the lateral sulcus (the fissure separating the temporal lobe from the parietal lobe, parietal and frontal lobes) within each brain hemisphere ...
and may be associated with recognizing a tone of voice in spoken native languages.
[ ] This expands on previous work
[ ] indicating that comprehension of
inflectional
In linguistic morphology, inflection (less commonly, inflexion) is a process of word formation in which a word is modified to express different grammatical categories such as tense, case, voice, aspect, person, number, gender, mood, anima ...
morpheme
A morpheme is any of the smallest meaningful constituents within a linguistic expression and particularly within a word. Many words are themselves standalone morphemes, while other words contain multiple morphemes; in linguistic terminology, this ...
processing is associated with the inferior frontal gyrus.
* Triangular part of inferior frontal gyrus (pars triangularis), (cortex between the ascending ramus and the horizontal ramus of the lateral sulcus). It may be associated with the ability to translate from a secondary or tertiary language back to one's native language.
[ ]
*
Orbital part of inferior frontal gyrus
The orbital part of inferior frontal gyrus also known as the pars orbitalis is the orbital part of the inferior frontal gyrus.
In humans, this region is bordered by the triangular part of the inferior frontal gyrus (pars triangularis) and, su ...
(pars orbitalis) (cortex inferior and anterior to the horizontal ramus of the lateral sulcus)
Cytoarchitecturally the opercular part of the inferior frontal gyrus is known as
Brodmann area 44
Brodmann area 44, or BA44, is part of the frontal cortex in the human brain. Situated just anterior to premotor cortex ( BA6) and on the lateral surface, inferior to BA9.
This area is also known as pars opercularis (of the inferior frontal gyr ...
(BA44). The triangular part of the inferior frontal gyrus is known as
Brodmann area 45
Brodmann area 45 (BA45), is part of the Frontal lobe, frontal Cerebral cortex, cortex in the human brain. It is situated on the lateral surface, inferior to Brodmann area 9, BA9 and adjacent to Brodmann area 46, BA46.
This area in humans occupies ...
(BA45), and the orbital part of the inferior frontal gyrus is known as
Brodmann area 47
Brodmann area 47, or BA47, is part of the frontal cortex in the human brain. It curves from the lateral surface of the frontal lobe into the ventral (orbital) frontal cortex. It is inferior to BA10 and BA45, and lateral to BA11. This cytoarc ...
. The opercular part and the triangular part (BA44 and BA45) make up
Broca's area
Broca's area, or the Broca area (, also , ), is a region in the frontal lobe of the dominant Cerebral hemisphere, hemisphere, usually the left, of the Human brain, brain with functions linked to speech production.
Language processing in the brai ...
.
Function
The inferior frontal gyrus has a number of functions including the
processing of speech and language in
Broca's area
Broca's area, or the Broca area (, also , ), is a region in the frontal lobe of the dominant Cerebral hemisphere, hemisphere, usually the left, of the Human brain, brain with functions linked to speech production.
Language processing in the brai ...
.
Neural circuitry has been shown to connect different sites of stimulus to other regions of response including other subdivisions and also other frontal gyri.
Language processing
The left opercular part of the inferior frontal gyrus is a part of the
articulatory network involved in motor syllable programs. The articulatory network also contains the
premotor cortex
The premotor cortex is an area of the motor cortex lying within the frontal lobe of the brain just anterior to the primary motor cortex. It occupies part of Brodmann's area 6. It has been studied mainly in primates, including monkeys and human ...
, and the anterior
insula. These areas are interrelated but have specific functions in speech comprehension and production. The articulatory network acts mostly when the
vocal tract
The vocal tract is the cavity in human bodies and in animals where the sound produced at the sound source (larynx in mammals; syrinx in birds) is filtered.
In birds, it consists of the trachea, the syrinx, the oral cavity, the upper part of t ...
moves to produce syllables. The pars opercularis acts indirectly through the
motor cortex
The motor cortex is the region of the cerebral cortex involved in the planning, motor control, control, and execution of voluntary movements.
The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately ...
to control the motor aspect of
speech production
Speech production is the process by which thoughts are translated into speech. This includes the selection of words, the organization of relevant Grammar, grammatical forms, and then the articulation of the resulting sounds by the motor system usi ...
, and codes motor programs for this system, while the
auditory cortex
The auditory cortex is the part of the temporal lobe that processes auditory information in humans and many other vertebrates. It is a part of the auditory system, performing basic and higher functions in hearing, such as possible relations to ...
(via the
temporoparietal junction
The temporoparietal junction (TPJ) is an area of the brain where the temporal and parietal lobes meet, at the posterior end of the lateral sulcus (Sylvian fissure). The TPJ incorporates information from the thalamus and the limbic system as well ...
in the lateral sulcus (Sylvian fissure) houses a series of sensory targets. Together, these areas function as a sensory-motor loop for syllable information coding.
In a study conducted comparing phonological and arithmetic processing and the involvement of different sections of the inferior frontal gyrus and angular gyrus, cortical activation for phonology, subtraction, and multiplication tasks was compared. The predetermined language-calculation network was limited to the left inferior frontal gyrus, angular gyrus, superior parietal lobule, and the horizontal portion of the intraparietal sulcus. The results were significant to support that there was a pattern of left lateralization for each of these tasks all activating the Perisylvian fissure network, with some general localized areas for phonology and arithmetic. It was supported that phonology activated the pars opercularis (BA44), and anterior angular gyrus, multiplication mainly implicated the pars triangularis (BA45), and the posterior angular gyrus. These systems are activated through similar neuronal processes but independently placed along the network.
Language comprehension and production
Most language processing takes place in
Broca's area
Broca's area, or the Broca area (, also , ), is a region in the frontal lobe of the dominant Cerebral hemisphere, hemisphere, usually the left, of the Human brain, brain with functions linked to speech production.
Language processing in the brai ...
usually in the left hemisphere. Damage to this region often results in a type of non-fluent
aphasia
Aphasia, also known as dysphasia, is an impairment in a person's ability to comprehend or formulate language because of dysfunction in specific brain regions. The major causes are stroke and head trauma; prevalence is hard to determine, but aph ...
known as
Broca's aphasia. Broca's area is made up of the pars opercularis and the pars triangularis, both of which contribute to verbal fluency, but each has its own specific contribution. The pars opercularis (BA44) is involved in language production and phonological processing due to its connections with motor areas of the mouth and tongue. The pars triangularis (BA45) is involved in semantic processing. Characteristics of Broca's aphasia include agrammatic speech, relatively good language comprehension, poor repetition, and difficulty speaking mostly uttering short sentences made up mostly of nouns. The left IFG has also been suggested to play a role in inhibitory processes, including the tendency to inhibit learning from undesirable information. For example,
transcranial magnetic stimulation
Transcranial magnetic stimulation (TMS) is a noninvasive neurostimulation technique in which a changing magnetic field is used to induce an electric current in a targeted area of the brain through electromagnetic induction. A device called a st ...
to the left IFG has been shown to release such inhibition, increasing the ability to learn from undesirable information.
The right opercular part of the IFG, (BA44) has been implicated in
go/no go tasks. In these tasks, the participant encounters a preliminary task (for instance repeatedly pressing a button), and then must halt this task whenever a "no go" signal is presented, ultimately measuring a level of impulse control through inhibition of a prepotent response. It seems that the same area is also implicated in risk aversion: a study found that higher risk aversion correlated with higher activity at IFG.
This might be explained as an inhibition signal to accept a risky option. Disruption of activity of this area with
transcranial direct-current stimulation
Transcranial direct current stimulation (tDCS) is a form of neuromodulation that uses constant, low direct current delivered via electrodes on the head. This type of neurotherapy was originally developed to help patients with brain injuries or ne ...
(tDCS) leads to change in risk attitudes, as behaviorally demonstrated by choices over risky outcomes.
Additional images
File:Inferior frontal gyrus coronal sections.gif, Inferior frontal gyrus highlighted in green on coronal T1 MRI images
File:Inferior frontal gyrus sagittal sections.gif, Inferior frontal gyrus highlighted in green on sagittal T1 MRI images
File:Inferior frontal gyrus transversal sections.gif, Inferior frontal gyrus highlighted in green on transversal T1 MRI images
References
External links
*
{{DEFAULTSORT:Inferior Frontal Gyrus
Gyri
Frontal lobe